A sleep mode of operation has been important to a successful deployment of modern wireless mobile devices. Sleep mode is a state wherein a mobile station (MS) refrains from communicating with a base station (BS) for a pre-negotiated period. During the sleep period, the MS may be generally unavailable to receive communications from the BS. Sleep mode may minimize MS power usage and conserve spectral resources.
When the MS is in the sleep-mode state, the BS may buffer or drop media access control (MAC) service data units (SDUs) addressed to a unicast connection bound to the MS. The BS may choose to delay a transmission of SDUs addressed to a multicast connection until an occurrence of an availability interval common to all MSs participating in the multicast connection.
A BS may maintain one or more contexts for each MS registered at the BS. Each context may comprise connection parameters related to a power-saving class. The power-saving class may comprise a group of connections with common quality-of-service demand properties. For example, in an Institute of Electrical and Electronics Engineers (IEEE) 802.16e™ network, all best-effort service (BE) and non-real-time variable rate service (NRT-VR) connections may be marked as belonging to a single class. Additional information regarding the IEEE 802.16e™ protocol standard may be found in 802.16e™: IEEE Standard for Local and Metropolitan Area Networks—Part 16: Air Interface for Fixed and Mobile Broadband Wireless Access Systems—Amendment 2: Physical and Medium Access Control Layers for Combined Fixed and Mobile Operation in Licensed Bands (published Feb. 28, 2006). Two unsolicited grant service (UGS) connections may belong to two different classes, in case the latter have different intervals between subsequent allocations. A power-saving class may be repeatedly activated and deactivated. Activation in this regard means starting sleep and listening window sequences associated with a class.
Three types of power-saving classes are defined in 802.16e™. They differ according to parameter sets, procedures for activation and deactivation, and policies to determine MS availability for data transmission. Power Saving Class type I is recommended for connections of a BE and an NRT-VR type. Power Saving Class type II is recommended for connections of a UGS and an RT-VR type. Power Saving Class type III is recommended for multicast connections and for management operations.
A challenge of sleep-mode operation is how to maximize sleep-mode intervals without degrading a quality and performance required by real-time services. Efforts have included fine tuning power-saving mechanisms, including methods of dynamic adaptation to a variety of traffic patterns and user behavior.